A common isolation enclosure used in the prior art is the glove box. At least three types of systems employing glove boxes are known: filter systems, negative systems, and positive systems. Filter systems are those connected to the ambient air by filters. Negative systems are those employing an isolated atmosphere at negative pressure in order to prevent the escape of dangerous materials. Positive systems are those having an isolated atmosphere at positive pressure to prevent the action of ordinary air on reactive materials inside the glove box.
In certain industries, such as the nuclear industry or the pharmaceutical industry, filter systems are used to isolate manufacturing processes from the ambient air, either to prevent the propagation of contaminant products into the atmosphere, or to prevent the introduction of pollutants contained in the atmosphere into the place where the manufacturing process is being performed. Glove boxes employed in such systems are typically ventilated by ventilation networks which permit the control of the rate of flow and of the pressure prevailing in each of them. In the ventilation network, when air is admitted and exhausted, one or more high-efficiency filtration barriers are installed in order to trap the polluting or radioactive dusts.
In negative pressure glove box systems, the gloves are always positioned inside the box. Such systems tend to be less troublesome than positive systems as far as pressure maintenance is concerned.
In positive glove box systems, the gloves typically protrude out of the glove box when not in use as a result of the positive pressure forcing them out. To use the gloves, the hand is inserted into them and the glove is forced into the glove box, against the positive pressure. Since the volume of the box is considerably decreased by the insertion of the glove, the pressure will go up, which results in the operator struggling to move the glove against the higher pressure. When the glove is pulled out, the sudden pressure drop poses a risk of leaks in the system.
To avoid these problems in positive systems and in some negative systems, the prior art has employed expensive valving systems to respond to the pressure changes to maintain a relatively constant pressure. Aside from their considerable expense, such valves tend to break down easily.
Typically, maximum and minimum pressure valves are employed, one connected to a gas source, the other to a vent to the ambient air. Both valves are connected to a pressure sensor. The sensor, valves, and isolation gas source are each a potential source of failure. In particular, failure of the maximum pressure valve could cause an excessively high pressure, which would rip the gloves off the glove box. Failure of the minimum pressure valve could result in a negative pressure, which would allow contaminating ambient air to leak in.
Thus, valves and attendant apparatus used in the prior art are a source of expense and potential breakdowns. Reducing or eliminating such valves would contribute to cheaper, safer systems. Additionally, it would be desirable to avoid waste and replenishment of the gas source used in connection with prior art systems.